CO2 cooling for particle detectors: experiences from the CMS and ATLAS detector systems at the LHC, and prospects for future upgrades.

CO2 cooling is the main candidate technology for the thermal control of the new generation semi-conductor particle detectors of the Large Hadron Collider (LHC) experiments at CERN. Two new CO2 cooling systems have recently been constructed for the ATLAS and CMS experiments. Both systems will cool the innermost detector layers; the ATLAS IBL system has a cooling capacity of 2.5 kW at -40°C and the CMS Pixel system has a capacity of 15kW at -25°C. Future upgrades of these experiments foresee the full replacement of the tracking detectors around 2024. These new, very large detectors – each about 200 m2 of semi-conductor sensors – will also be cooled with CO2. Studies to scale up the current design concepts and technologies to cooling powers of about 150 kW have started. This paper describes the CO2 cooling activities at CERN, profiting of the know-how gained during the design, construction and commissioning of the ATLAS IBL and CMS Upgrade Pixel cooling systems. Experiences of special adopted solutions will be discussed such as vacuum insulated triple coaxial transfer lines, redundancy solutions, hydraulic components, system monitoring and control approach and evaporator line fluid distribution. A prospect of the future will be given describing the needs for the development of the large systems as well as the development of mobile test equipment such as laboratory units, which are needed for the detector prototyping phases at many laboratories around the world.

二氧化碳（CO₂）冷却技术是欧洲核子研究中心（CERN）大型强子对撞机（Large Hadron Collider，LHC）实验的新一代半导体粒子探测器热控的主流候选技术。近期，针对ATLAS与CMS实验，两套全新的二氧化碳冷却系统已建成投用。两套系统均将用于冷却最内层探测器模组：ATLAS插入式像素探测器（IBL）系统在-40℃工况下的制冷量可达2.5kW，CMS像素探测器系统则在-25℃工况下拥有15kW的制冷能力。该两项实验的未来升级计划预计于2024年左右全面替换现有跟踪探测器。这些全新的超大型探测器——单台探测器的半导体传感器面积约达200平方米——同样将采用二氧化碳冷却方案。目前，针对将现有设计理念与技术扩容至约150kW制冷量的相关研究已正式启动。本论文阐述了欧洲核子研究中心开展的二氧化碳冷却相关工作，依托ATLAS IBL与CMS升级像素冷却系统在设计、搭建与调试阶段积累的技术诀窍。文中将讨论特殊定制解决方案的实践经验，包括真空绝热三重同轴传输管线、冗余设计方案、液压元件、系统监测与控制策略，以及蒸发器管路流体分配方案。最后将对未来发展进行展望，阐述大型冷却系统的研发需求，以及面向全球众多实验室的探测器原型阶段所需的移动式测试设备（如实验室测试单元）的开发方向。